Infra-red gas burner structure



Nov. 7, 1967 J. J. FANNON, JR 3,

INFRA-RED GAS BURNER STRUCTURE Filed Sept. 11:, 1964 5 Sheets-Sheet 1FIG. I

INVENTOR JOHN J. FANNON ,1 'JR.

BY/W MQQM ATTORNEYS Nov. 7, 1967 J. J. FANNON, JR

INFRA-RED GAS BURNER-STRUCTURE 5 Sheets-Sheet Filed Sept. 11, 1964 INVENTOR JOHN J. FAA/MON, JR.

ATTORNEYS J. J. FANNON, JR

INFRA-RED GAS BURNER STRUCTURE 7 Nov. 7, 1967 Filed Sept; 11, 1964 5Sheets-Sheet, 5

INVENTOR JOHN J. FAN/VON, JR.

ATTORNEYS Nov. 7, 1967 J. J. FANNON, JR

INFRA-RED GAS BURNER STRUCTURE 5 Sheets-Sheet 4 Filed Sept. 11, 1964INVENTOR JOHN J. FAN/V0, JR.

BY MM MO M ATTORNEYS 1957 J. J. FANNON, Jr 3,351,043

INFRA-RED GAS BURNER STRUCTURE Filed Sept. 11, 1964 5 Sheets-Sheet 5FIG. /.9

ATTORNEYS United States Patent 3,351,048 INFRA-RED GAS BURNER STRUCTUREJohn J. Fannon, Jr., Grosse Pointe Park, Mich., assignor,

by mesne assignments, to Fostoria-Fannon, Inc., a corporation of OhioFiled Sept. 11, 1964, Ser. No. 395,839 6 Claims. (Cl. 126-92) Thisinvention relates to improved line burners and to methods of producingsuch burners.

Application No. 370,795, now abandoned filed May 28, 1964, by Arthur C.W. Johnson discloses line type infrared generators in which acombustible fuel-air mixture flows from a plenum or distribution tubethrough a ribbon type orifice grid and burns on the outer surface of thegrid. The heat liberated by the combustion of the fuel-air mixture istransferred by radiation and convection to a radiating and reradiatinggrid overlying the orifice grid, heating it to incandescence. Theincandescent grid emits infrared radiation, part or" which is directedonto the articles or into the area to be heated and the remainder ofwhich is reradiated to the distribution tube and orifice grid, raisingthe operating temperature of the burner. This increases the tendency ofthe flame to flash back into the distribution tube and ignite thecombustible mixture in the tube, resulting in damage to or destructionof the burner. Also, as the rate at which the cornbustible mixture issupplied to such burners is increased to raise operating temperatures,the tendency for the flame to flash back into the distribution tubeincreases.

Another disadvantage of the devices disclosed in the Johnson applicationis that their heat output is only in the form of radiant energy exceptfor one particular embodiment which is, however, useful only forspecialized purposes. Consequently, they are unsuitable for use innumerous processes and types of heating apparatus requiring circulationof the combustion products, direct flame radiation, or flameimpingement, for example.

One important object of the present invention is, therefore, theprovision of novel improved line burners adapted for use in a widevariety of heat transfer devices and processes at temperatures up to2000 F. or higher.

In conjunction with the foregoing object, another important object ofthe present invention is the provision of novel improved line burnersadapted for use in heating devices requiring transfer of heat by directradiation from, contact with, or circulation of the burning gases aswell as those requiring heat output in the form of infrared radiationfrom an incandescent radiant member.

In conjunction with the foregoing, other important objects of thepresent invention include the provision of novel, improved line burnerswhich:

(1) Are capable of operating at higher temperatures than prior artburners of this general type and are capable of converting a higherpercentage of the heat value in the fuel employed into usable heat thanhas heretofore been possible;

Consist primarily of sheet metal and are easily assembled and have othercharacteristics which make them readily producible at low cost by massproduction techniques;

(3) Are easy to install and service and have a long useful life;

(4) Are not adversely effected by the unequal expansion of theircomponents which occurs as they heat up and cool off;

(5) Have orifice grids (or other orifice structures) that are easilyremovable for cleaning or replacement;

(6) Are virtually free from flashback, even when the ambient temperatureis as high as 1500 F.;

i (7) In conjunction with the preceding object, have a novel combinationand relative disposition of distribution tube and orifice grid and anovel arrangement for holding the foregoing components together thatminimizes eating of the fuel-air distribution tube;

(8) In conjunction with object 6), have a novel, small diameter,insulated distribution tube construction which minimizes the transfer ofheat to the tube, especially when the burner is operated in extremely:hot environments; and

(9) Are particularly adapted to installation in home heating plants.

Other important objects of this invention are the provision of novel,improved infrared generators which employ line burners in accord withthe principles of the present invention and which:

(1) Are capable of producing emitted energy of wave lengths readilyabsorbed by most materials;

(2) Include novel reflector structure which efiiciently projects theradiation emitted from the radiant grid in the desired pattern anddirection or directions;

(3) Are applicable to a wide variety of processes such as the heating ofsheets and continuous webs, the baking or drying of many types offinishes and coatings, the heating of objects on conveyors, and theheating of rolls and platens; which may be employed in a wide variety ofheating apparatus such as various types of ovens and furnaces; and whichare particularly suited to applications where high concentrations ofradiant energy are required;

(4) Are particularly suited for indoor and outdoor area heating; and

(5) Can use either metallic or ceramic grids.

Other important objects of the present invention reside in the provisionof novel methods for manufacturing line burners and infrared generatorsin accord with the preceding objects.

The line burners of the present invention, by which these importantobjects are attained, include a sheet metal fuel-air plenum ordistribution tube of novel configuration which reduces heat dissipation,thereby increasing operating efiiciency; is rigid and strong, therebyassuring long operating life; and is easily formed, thereby contributingto lower manufacturing costs. By attaching the orifice structure to thedistribution system in a novel manner described in detail hereinafter,the orifice structure is made readily detachable for cleaning orreplacement, so that the line burners disclosed herein are easy andinexpensive to service.

In addition, the line burners of the present invention preferably employa novel relative disposition of distribution tube and orifice grid and anovel arrangement for holding the distribution tube and orifice gridtogether which, together with the distribution tube configuration justmentioned, virtually eliminate the problem of flashback. This remainstrue even though the burner is crowded (i.e., the combustible mixture issupplied at an abnormally high rate to obtain maximum heat output and/ortemperature), is of an extremely long length, or is operated at itslowest rate facing downward.

Another important advantage of the novel line burners just described isthat they are capable of operating in extremely hot environments(ambient temperatures of 1500 F. or higher). In addition, these burnershave a long service life and are useful in a wide variety of heatemploying processes and in many different types of ovens, furnaces, andother heating apparatuses, including those intended for home use.

A further important feature ofthe present invention is the use of arelatively small diameter, insulated distribution tube. The reduction indiameter of the tube increases the velocity at which the combustiblemixture flows through the tube, increasing the rate at which heat istransferred from the tube to the mixture, and also re duces the area ofthe tube exposed to the ambient atmosphere, which reduces the rate atwhich heat is transferred from the ambient atmosphere to the tube. Thetube insulation further reduces the rate at which heat is transferredfrom the ambient atmosphere to the tube. The net result of the foregoingfactors is that the distribution tube remains cooler than it otherwisewould and the possibility of flashback is even further reduced. This isextremely important in applications where overheating is most likely tooccur such as where the burner is operated in an inverted orientationand in an extremely hot environ mentfor example, in an oven or furnacewhere the ambient temperature may be 1500 F. or higher.

The novel line burners of the present invention also represent anadvance in the art in that they may be readily converted into improvedinfrared generators simply by the addition of a radiant grid, which maybe of either the metallic or the ceramic type. In the present inventionthe novel mounting arrangement by which the orifice grid is attached tothe distribution tube also supports the radiant grid from thedistribution tube in a manner which permits the radiant grid to expandfreely as the infrared generator heats up and cools off. This preventsthe radiant grid from warping, which materially increases the life ofthe infrared generator.

The novel combination of components described briefly above has beenfound to result in an infrared generator of high efficiency and outputand one which can readily be provided with reflectors capable ofefficiently concentrating the emitted radiant energy in a beam ofdesired configuration and directing it in the desired direction ordirections. The infrared generators of the present invention are usefulin a wide variety of heat employing processes and in many differenttypes of heating devices, especially those requiring a highconcentration of radiant energy. These infrared generators are alsoparticularly suitable for indoor and outdoor area heating. Moreover, theinfrared generators of the present invention emit radiant energy in arange of wave lengths which is such that the emitted radiant energy isreadily absorbed by most materials. For example, with the radiant gridat a temperature of 2000 F., 96% of the emitted radiation has a wavelength in the range of 1-7 microns and is readily absorbed by mostmaterials.

Additional advantages, other objects, and further novel features of thepresent invention will become apparent from the appended claims and asthe ensuing detailed description and discussion proceeds in conjunctionwith the accompanying drawing, in which:

FIGURE 1 is a generally diagrammatic section through a line burnerconstructed in accordance with the principles of the present inventionand the combustion chamber of a furnace in which the burner may beemployed;

FIGURE 2 is a side view of the line burner of FIG- URE 1:

FIGURE 3 is a side view of an infrared generator embodying the lineburner of FIGURE 1 with portions of several components being broken awayto better show the construction of the infrared generator;

FIGURE 4 is a section through the infrared generator of FIGURE 3, takensubstantially along line 44 of the latter figure;

FIGURE 5 is a fragmentary view of a radiant grid employed in theinfrared generator of FIGURE 3, looking in the direction of arrows 55 ofFIGURE 4;

FIGURE 6 is a transverse vertical section through a modified form ofinfrared generator;

FIGURE 7 is a fragmentary view of an orifice grid employed in the lineburner of FIGURE 3, looking in the direction of arrows 7-7 of FIGURE 4;

FIGURE 8 is a view, similar to FIGURE 7, of a modified form of orificegrid;

FIGURE 9 is a perspective view of radiant grid supporting clips employedin the infrared generator of FIG- 4 URE 3 and of a portion of the gridsupported by the clips;

FIGURE 10 is a side view of a modified form of line burner constructedin accord with the principles of the present invention;

FIGURE 11 is a section through the line burner generator of FIGURE 10,taken substantially along line 11-11 of the latter figure;

FIGURE 12 is a fragmentary plan view of a modified orifice structurewhich may be employed in the line burners of the present invention andthe distribution tube to which it is attached, looking in the directionof arrows 12-12 of FIGURE 13;

FIGURE 13 is a sectional view of the distribution tube and orifice,taken substantially along line 13-13 of FIG- URE 12;

FIGURE 14 is a fragmentary perspective view of the orifice structureshown in FIGURES 12 and 13;

FIGURE 15 is a view, similar to FIGURE 13, of a further form of orificestructure and the distribution tube to which it is attached;

FIGURE 16 is a section through the orifice structure of FIGURE 15, takensubstantially along line 16-16 of FIGURE 15;

FIGURE 17 is a section through an infrared generator constructed inaccord with the principles of the present invention employing aninsulated distribution tube which is especially resistant to overheatingand a ceramic radiant grid;

FIGURE 18 is a section through a second form of insulated distributiontube; and

FIGURE 19 is a section through a third form of distribution tube.

Referring now to the drawing, in which exemplary embodiments of thepresent invention are shown, FIG- URE 1 depicts a conventional warm airfurnace 20 having a combustion chamber 22 in which a line burner 24constructed in accord with the principles of the present invention ismounted by brackets 26. Line burner 24 includes a fuel-air mixturedistribution tube 28 and an orifice grid 30, through which the fuel-airmixture flows from the interior of distribution tube 28 to a combustionzone adjacent the outer end 32 of the grid.

Combustion air is supplied to line burner 24 by a combustion air blower34, the outlet of which communicates through a fuel-air supply conduit35 with the interior of distribution tube 28. Fuel is supplied through aconduit 36 terminating in an orifice 38 in conduit 35 and mixes with theblower supplied air to form a combustible mixture. Burner 24- may beoperated on primary air supplied by blower 34 or secondary air can besupplied to the combustion zone in accord with conventional practice.

Furnace 29, by itself, is not part of the present invention and is shownmerely to illustrate a typical application of the novel line burnersdisclosed herein. Typically, the furnaces combustion chamber 22 wouldcommunicate with the atmosphere through ports 40, through whichsecondary combustion air could enter, and a chimney or flue, throughwhich combustion products would be discharged. The combustion chamber isconventionally surrounded by a plenum through which air is blown to heatit.

As shown in FIGURE 1, the distribution tube 28 has a generallydiamond-like configuration with the two flanges 54 and 56 lying inparallel spaced apart relationship and providing an outlet passage 64from the interior to the exterior of the distribution tube. This flangedconfiguration is of substantial importance in that it materially reducesthe amount of usable heat dissipated through distribution tube 28 fromthe combustion zone and correspondingly increases operating efiiciency.

Sheet metal end members 66 and 68 (see FIGURE 3) are fixed to theopposite ends of distribution tube 28 to prevent the escape of thecombustible mixture. An aperture 7ft in end member 68 providescommunication he-' tween the interior of the tube and supply conduit 35,through which the combustible fuel-air mixture flows into distributiontube 28.

"Orifice structure 30, through which the fuel-air mixture flows fromdistribution tube 28, is mounted in the outlet passage 64 of fuel-airdistribution tube 28 between flanges 54 and S6 to prevent the flame fromflashing back from the combustion zone through passage 64 into fuelairmixture distribution tube 28.

The illustrated orifice grid 30 is of the ribbon type, and consists ofembossed metallic ribbons which provide a number of small passagesextending between and opening onto the opposed lateral edges of theassemblage of ribbons. The particular configuration of the individualribbon is not critical in the present invention; and the length andtotal area of the lateral passages may be varied as desired forparticular applications of this invention. It is necessary, however,that the lateral passages be sufliciently small in diameter andsufficiently long that flame cannot flash back through the passages fromthe combustion zone adjacent the face 32 of the orifice structure to theinterior of distribution tube 28. In addition, the total area of theopenings must be sufiiciently great that the combustible mixture willflow from distribution tube 28 to the combustion zone in sufiicientquantity to maintain the desired rate of combustion.

One suitable ribbon type orifice structure, illustrated in FIGURE 7,consists of metallic ribbons 72 in which laterally extendingsemicircular depressions or convolutions 74 are formed at periodicintervals and are typically on the order of 0.188 inch apart. As shownin FIGURE 7, metallic ribbons 72 are arranged in two groups 76 and 78.In each group, depressions 74 extend in the same direction so that thedepressions 74 of the ribbons 72 in each group are nested. The twogroups 7-6 and 78 are assembled in mirror image relationship, and theindividual ribbons 72 pinned or brazed together at opposite ends oforifice structure 30 to maintain them in the correct position relativeto each other.

As shown in FIGURE 7, the construction just described provides anorifice structure having lateral passages 80 between adjacentdepressions 74, lateral passages '82 between the adjacent planarportions of the ribbons between depressions 74, lateral passages 84formed by the opposed depressions 74 of the two innermost ribbons 72 ingroups 76 and 78, and Lateral passages 86 between the two outermostribbons 72 and the associated distribution tube flanges 54 and 56.

Typically, ribbons 72 will be 0.375 inch wide; and passages 80, 82, 84,and 86 will therefore be 0.375 inch long. Passages 80 and 82 may be onthe order of 0.010 inch wide and passages 84 on the order of 0.050 inchin diameter. The passages 86 of a typical grid structure may be on theorder of 0.025 inch Wide.

As this grid structure, by itself, forms no part of the presentinvention and as it is disclosed in detail in copending application No.370,795, mentioned above, to which reference may be had, if desired, itis not believed necessary to describe it in more detail herein.

Orifice structure 30 is removaly retained between distribution tubeflanges 54 and 56 by studs 100 and straps 102 (see FIGURE 3). Studs 100,which extend laterally through the apertures 44 in distribution tubeflanges 54 and 56 at intervals (commonly on the order of 6") along thedistribution tube, locate orifice structure 30 relative to the inner end104 of the passage 64 between distribution tube flanges 54 and 56.Retainers 106, threaded on the opposite ends of studs 100, clamp flanges54 and 56 against orifice structure 30 to removably retain it in passage64. Straps 102 (which prevent orifice structure 30 from dropping out ofpassage 64) are provided at the ends of distribution tube 28. Straps 102extend between distribution tube flanges 54 and 56 and are fixed to theflanges as by brazing.

Orifice structure 30 can be removed from line burner 24 merely byloosening retainers 106 and sliding the orifice structure lengthwise outof the passage 64 between distribution tube flanges 54 and 56. This isan important feature of the present invention since it facilitates theremoval of orifice structure 30 for cleaning or replacement.

The novel line burners just described have a number of desirablecharacteristics which are not possessed by prior art burners. Theseburners may be used in infrared generators to heat radiation emittingmembers up to 2200 F. or higher and in burner lines more than ten feetlong without unacceptable distortion of their components or flashback.At the same time, these burners are of light weight, are economical tomanufacture, and, when used in infrared generators, are capable ofmaintaining uniform temperatures over the entire radiation emittingsurface of the radiant member.

These heretofore unattainable operating characteristics are due, inlarge part, to the following features of these burners:

(A) Only extremely small areas of distribution tube 28 and orifice grid30 are exposed to radiation from the burning gases (and the radiantmember if the line burner is incorporated in an infrared generator) asthe only portions of these components exposed to such radiation are thethin outer edges of distribution tube flanges 54 and 56 and the edges ofthe ribbons 72 in orifice structure 30. This minimizes heating of thesecomponents, minimizing the possibility of flashback and reducing thedissipation of usable heat.

(B) The passages 80, 82, 84, and 86 through orifice grid 30 have verysmall cross sectional dimensions in comparison to their length. Forexample, as indicated previously, these passages may typically range inwidth from 0.025 to 0.010 inch wide and have a length of 0.375 inch sothat the minimum ratio of length to Width is 37.521. This materiallyreduces the possibility of flashback in comparison to prior art burnerssuch as those shown in co pending application No. 370,795, which employdistribution tubes of pipe and in which the outlet passages are slotsmilled in the wall of the pipe. Even though ribbon type orifice gridsare employed with such distribution tubes, the controlling factor is theratio of slot depth (equal to the wall thickness of the pipe) to thewidth of the slot, a ratio much lower than the effective depth to widthratios of the present invention.

(C) The large number of ports provided by the ribbon length of theburner with minimum mixture pressure.

velocity of the gas flowing through the ports in the orifice grid, whichfurther reduces the posslbility of flashbac (E) Flanges 54 and 56 whichseparate distribution tube 28 from the combustion zone adjacent theouter face 32 of orifice grid 30 and limit the path along which heat canbe conducted from the combustion zone to the walls 50, 52, 57, and 58 ofthe distribution tube to one of substantial length and small crosssection, minimizing, the conduction of heat to the walls of thedistribution tube. This, too, reduces the possibility of flashback andthe dissipation of usable heat. In addition, the flow of the combustiblemixture through the passages 86 between the outermost ribbons 72 oforifice grid 30 and the flanges cools the latter, further reducing thetransmission of heat to the walls of the distribution tube with theattendant beneficial results mentioned above.

(F) The cooling action of the stream of combustible mixture movingthrough distribution tube 28 at high velocity and entering the ports inorifice grid 30 through the narrow outlet passage 64 between flanges 54and 56 which removes substantial heat from the distribution tube walls.Since these passages have small cross sectional areas, the pressure dropacross the orifice grid is relatively large, materially increasing thevelocity of the flow through tube 28 and the elfectiveness of the actionof the mixture in Wiping across the walls of the tube, both of whichmaxirnize its cooling effect.

By the combination of novel features described above, distribution tube28 can be maintained at temperatures as low as 300400 F. even thoughline burner 24 is incorporated in an infrared generator in which theradiant member is at a temperature of 18002000 F. or higher. Thisvirtually eliminates the possibility of flashback and results in a moreefficient burner than those heretofore available.

Another line burner constructed in accord with the principles of thepresent invention, which may be preferable for particular applications,is shown in FIGURES and 11 and identified by reference character 108. Inthese figures, like reference characters have been employed to identifyline burner components which are identical to those of the line burner24 illustrated in FIGURES 1 and 2.

This embodiment of the present invention employs a fuel-air distributiontube 110 which has a circular configuration rather than the diamondconfiguration of fuelair distribution tube 28. As in the previouslydescribed line burner embodiment, the fuel-air distribution tube haslateral edge portions or flanges 112 bent at angles to the main body ofthe tube in parallel, spaced apart relation to provide a passage 114between the interior and exterior of the tube. Orifice grid 30, whichmay be of any of the constructions described above or hereinafter, ismounted in passage 114 between flanges 112 in the manner previouslydescribed.

End members 116 and 118 (see FIGURE 10) are brazed or otherwise fixed toopposite ends of fuel-air distribution tube 110 to prevent the leakageof the combustible mixture. As in the previously described line burner24, the combustible fuel-air mixture is fed into distribution tube 110through a fuel-air supply conduit 120 extending through an aperture 122in distribution tube end member 118.

FIGURES 12-14 and 18 and 19 illustrate modified g rid structures which,if desired, may be employed in line burners constructed in accord withthe principles of the present invention. For the sake of convenience,they will be described in conjunction with line burners of the typeshown in FIGURES 1 and 2. This description is not intended to belimiting, however, as these grid structures are generally applicable toline burners constructed in accord with the principles of thisinvention. The orifice grid structure 123 illustrated in FIGURES 12-14is a channel having legs 124 connected by a web 126 in which narrow,laterally extending slits 128 are formed. Channel 123 is fixed inpassage 64 between flanges 54 and 56 of fuel-air distribution tube 28 inthe manner described in conjunction with the embodiment of FIGURES 3 and4; and the combustible mixture flows from the interior of thedistribution tube through passage 64 and the slits 128 in channel 123 tothe combustion zone adjacent the outer face 130 of the channel.

As shown in FIGURE 14, blocks 132 are fixed in the ends of channel 123to prevent the combustible mixture from leaking through the open ends ofthe channel.

' This form of orifice grid does not prevent flashback as effectively asthe ribbon type orifice grid described previously. However, it issubstantially less expensive than the latter; and, where operating andother conditions are such that there is little tendency for flashback,the channel type of orifice grid is entirely satisfactory.

Many modifications may be made in the illustrated channel 123. Forexample, the size of the channel and the material from which it isformed may be varied as may the size of slits 123. Also, circular orother shapes of holes may be substituted for the narrow elongatedrectangular slits shown, if desired.

The orifice structure 134 shown in FIGURES and 16 consists of twoidentical channels 136 and 138 of the type just described arranged inthe passage 64 between 8 flanges 54 and 56 of fuel-air distribution tube28 in backto-back relationship with their legs 140 juxtaposed. Thisprovides aligned slits 142 and 144 spaced longitudinally of passage 64,an arrangement which is highly effective in preventing flashback.

Another type of orifice grid structure, which functions particularlywell, is illustrated in FIGURE 8 and identified by reference character146. Grid structure 146 is formed from metallic ribbons 148 in whichlaterally extending triangular convolutions 150 are formed at periodicintervals. Ribbons 148 are assembled in pairs with the two ribbons ineach pair being disposed in mirror image relationship. The pairs ofribbons are assembled in side-by-side relationship with the convolutions150 of one pair midway between the convolutions 150 of the adjacentribbon pair. The ribbons 148 of grid structure 146, like the ribbons 72of grid structure 30, are preferably pinned or brazed together atopposite ends of the grid structure to give the latter structuralintegrity.

This arrangement provides lateral passages 154 between the associatedconvolutions 150 of the two ribbons in each pair; lateral passages 156,which are defined by the juxtaposed convolutions 150 of ribbons inadjacent ribbon pairs and the portions of the juxtaposed ribbons inadjacent pairs intermediate the convolutions; and lateral passages 158between the outermost ribbons 148 and flanges 54 and 56.

The various dimensions of the orifice structure 146 illustrated inFIGURE 8 may be similar to the corresponding dimensions of orificestructure 30. However, as discussed above, the particular dimensions arenot critical, it only being necessary that they be so selected as toprevent flashback and to accommodate flow of the combustion mixture atthe desired rate.

Line burners constructed in accord with the principles of the presentinvention may be readily converted into highly efiicient infraredgenerators by the addition of a radiant grid. To illustrate this aspectof the present invention, reference will be made to the conversion intoan infrared generator of the line burner shown in FIG- URES 1 and 2. Itis to be understood, however, that the line burner of FIGURES 10 and 11and other line burners constructed in accord with the principles of thisinvention may be similarly adapted to the production of infraredradiation.

Referring again to the drawing, FIGURE 3 illustrates an infraredgenerator 160 which includes the line burner 24 described previously anda radiant grid 162. Radiant grid 162, which is heated to incandescenceby the combustible mixture flowing through orifice structure 30 andburning adjacent its outer face 32 and emits the radiant energy desiredfor space, article, or other heating, is preferably of the aperturedconstruction disclosed in copending application No. 370,795. In thepresent invention, however, radiant grid 162 is made of a sheet of heatresistant metal such as Inconel or Hastaloy-X or a coated alloy and isbent into a horseshoe configuration providing a radiation emitting body164 and inturned mounting flanges 166 extending toward each other fromopposite sides of the radiation emitting body. In the embodiment of thepresent invention illustrated in FIGURES 3 and 4, the body 164 of grid162 has a radius of 0.75 inch and a height of 1.25 inches; and legs orflanges 166 are 0 .50 inch wide. This configuration is an importantfeature of the present invention as it provides a grid which isuniformly heated, which is extremely rigid and resistant to distortion,and which minimizes the dissipation of usable radiation to the fuel-airdistribution tube.

As best shown in FIGURES 4 and 9, the body 164 of radiant grid 162 isformed by stamping or other process into a configuration in which loops168 are displaced from the plane of the sheet from which the grid isformed at regular intervals to form openings extending normal to thesheet through which the combustion products may pass from the combustionzone. As discussed in detail in copending application No. 370,795, thisresults in a grid which is a highly eflicient emitter of infraredradiation and which effectively protects the flame from air currents ofsufficient strength to quench or snuff it out.

In flanges 166, loops 168 are preferably flattened back into the planeof the flanges or are omitted to provide flat flanges which can bereadily clamped between the hereinafter members employed to attach grid162 to distribution tube 28.

Referring now specifically to FIGURE 4, ears 170 are bent from grid body164 at its ends; and grid end plates 172 are spot welded to ears 170.End plates 172 support the open ends of the grid 162 and maintain thebody of the grid in the desired shape. They also prevent disturbance ofthe flame by air currents.

An aperture 174 may be provided in one or both of the end plates 172 tofacilitate lighting the burner, to accommodate a spark plug or flamesensor, and/or to allow flame to travel from one radiant grid to thenext adjacent radiant grid in an infrared generator having multipleradiants and adapted to be ignited at one end.

Grids 162 may be of any desired length. However, grids having a maximumlength of 24 inches are preferred since such shorter grids arepractically free of distortion due to expansion at high operatingtemperatures; and, if desired, longer infrared generators can readily beprovided by connecting shorter ones in end to end relationship to asingle longer distribution tube 28.

Referring now to FIGURES 3, 4, and 9, radiant grid 162 is removablyattached to the flanges 54 and 56 of fuel-air distribution tube 28 bycooperating pairs of inner and outer grid clamps or clips 178 and 180.As best shown in FIGURE 9, inner clip 178 has an L-shaped configurationprovided by two normally extending integral legs 182 and 184. Outer clip180 has a first leg 186 adapted to be fixed to leg 182 of clip 178, asecond leg 188 extending at right angles to leg 186 in parallel, spacedrelationship to leg 184 of clip 1'78, and a third integral leg 190.inclined at an angle to leg 188 and adapted to embrace the exterior ofradiant grid 162.

A pair of clips 178 and 180 is employed on either side of infraredgenerator 160 at each of the studs 100, which extend through alignedapertures 192 in clips 178 and 194 in clips 180. In the preferred mannerof assembling infrared generator 160, the clips 178 and 180 of each pairare spot Welded together and slid onto the associated flange 166 ofradiant grid 162 before end plates 172 are attached to the grid bymoving them in the direction shown, the associated mounting flange 166passing between leg 184 of clip 178 and leg 188 of clip 180 and theperipheral region of the grid body 164 passing between the edge of leg184 of clip 178 and leg 190 of clip 180. The end plates 172 are thenattached, the clip pairs assembled on studs 100, and retainers 106threaded on the studs to retain grid 162 in place.

In the assembled infrared generator 160 the space between each pair ofclips 178 and 180 is slightly greater than the thickness of theassociated flange 166. This permits longitudinal movement of flange 166between the clips of the parts expand or contract due to temperaturechanges, but restrains the flange and grid against appreciabletransverse movement. This permits grid 28 to expand axially as itstemperature increases, which prevents it from becoming distorted as itexpands and contracts longitudinally. Lateral expansion is accommodatedby the horseshoe configuration of the radiant grid so that the grid isalmost entirely free from expansion and contraction induced distortions.

Reflectors 198 are preferably employed in infrared generator 160 to formthe infrared radiation emitted from grid 162 into a beam of the desiredconfiguration and to project the beam in the desired direction ordirections. These reflectors may be formed from sheets of aluminizedsteel or any other good reflector of infrared radiation. Reflectors 198each have a main reflecting portion 200 and a mounting leg 202 connectedby an integral leg 204 extending upwardly and outwardly from mountingleg 202. Mounting leg 202 is provided with apertures (not shown) throughwhich mounting studs extend. Retainers 206, threaded on the outer endsof studs 100, secure reflectors 198 on studs 100 against retainers 106with the reflecting portion 200 of the two reflectors inclined outwardlyrelative to radiant grid 162 to concentrate the infrared radiationemitted from the grid in a downwardly directed beam toward the area oronto the objects to be heated by infrared radiation (reflecting portions200 of reflectors 198 are inclined at an angle of 45 to the horizontalin the embodiment of the invention illustrated in FIGURE 7, but thisangle is not critical).

As shown in FIGURE 4, the legs 204 of reflectors 198 connectingreflecting bodies 200 and legs 202 are inclined upwardly at acute anglesto mounting legs 202 with reflectors 198 assembled on studs 100. This isimportant in that radiant energy emitted from grid 162 and impinging onintermediate legs 204 is reflected downwardly and away from flanges 54and 56 of distribution tube 28. This reduces the transmission of heat todistribution tube 28 and, therefore, the dissipation of usable heat,increasing the infrared generators usable heat output and minimizing thepossibility of flashback.

Like radiant grids 162, reflectors 198 are preferably made in sizes notexceeding about 24 inches by length to prevent expansion and contractionfrom warping them.

The particular reflector configuration just described is merelyexemplary; and the angle of inclination of the reflectors main portions200 and the shape of the reflectors can be changed as desired to providethe desired pattern of radiant energy distribution. For example,reflectors having a parabolic or elliptical cross section could besubstituted for those illustrated in FIG- URE 3. As further examples,the reflector can be formed so that its main portion is normal to theaxis of the burner or lies in the plane and forms a continuation of thereflectors mounting leg.

In conjunction with the foregoing, infrared generator is illustrated inan orientation in which it directs the radiant energy emitted fromradiant grid 162 in a downward direction. However, the generator mayequally well be disposed in other orientations to direct the beam ofradiation upwardly or laterally, or at any desired angle to thehorizontal.

Many modifications may be made in the embodiments of the presentinvention described above to adapt the present invention to particularapplications. For example, certain infrared applications require thatthe radiant energy be confined to a narrow beam to, for example, providea highly intense concentration of the radiant energy over a narrow area.An embodiment of the present invention, designed to produce a narrowintense beam of infrared radiation, is illustrated in FIGURE 6 andidentified by reference character 208 (insofar as the components ofinfrared generator 208 are the same as those of infrared generator 160,they have been identified by like reference characters).

Refer-ring now to FIGURE 6, infrared generator 208 differs from infraredgenerator 160 primarily in the configuration of its radiant grid 210which, in this embodiment of the present invention, has a squareconfiguration provided by radiation emitting face 212 of the ribbedconstruction described above in conjunction with radiant grid 162,imperforate side walls 214 extending normally from opposite edges of theradiation emitting face, and imperforate flanges 216, extending normalto side Walls 214 from the edges thereof opposite radiant energyemitting face 212. Radiant grid 210 is preferably of one-piececonstruction since unitary construction provides maximum strength,simplifies manufacture, and minimizes distortion as the radiant grid isheated and cooled. To

prevent the dissipation of heat in lateral directions, insulatingmembers of Fiberfax or metal shields identified by reference character218 are preferably fixed to the inner surfaces of the side walls 214 ofradiant grid 210.

Grid 210 is assembled to fuel-air distribution tube 28 by pairs of clipsincluding a clip 178 and a clip 220, which is identical to the clip 180illustrated in FIGURE 9, except that the leg 222 of clip 220 is bent atright angles to the adjacent leg 224 to match the configuration of sidewalls 214 of radiant grid 210.

To further prevent the dissipation of heat to the sides of infraredgenerator 208, reflectors 226 may be fixed, in any desired manner, tothe side walls 214 of radiant grid 210 after it is assembled todistribution tube 28. Although the illustrated reflectors 226 haveplanar reflecting surfaces, the reflectors may as easily be formed inother configurations to alter the pattern of radiant energy emitted fromradiant grid 210.

FIGURE 17 illustrates an infrared generator 228, constructed in accordwith the principles of the present invention, which is particularlyadapted "for use in high temperature environments; e.g., in ovens or infurnaces where the temperature of the ambient atmosphere may typicallybe lSOO F. or higher. To the extent that infrared generator 228 and itscomponents are like those of previously described embodiments of thepresent invention, they will be identified by the same referencecharacters.

Infrared generator 228 differs from those previously described primarilyin the construction of its combustible mixture distribution tube 230 andits radiant grid 232.

Combustible mixture distribution tube 230 is identical to thedistribution tube 110 of the embodiment of the present inventionillustrated in FIGURE 11 except: (1) it has a smaller internal diameterand less exposed surface area; and (2) it has an internal insulatinglining 234. Lining 234 is preferably made of a material having low heatconductivity and may typically be a coat of refractory cement, enamel,or other suitable material which will adhere to the tube wall or a sheetof asbestos Fiberfax, or other insulating material cemented or otherwisesecured to the tube wall.

Both the reduced internal tube diameter and exposed surface area and theinsulating lining 234 are important in securing satisfactory operationin high temperature environments. Because of the smaller cross-section,combustible mixture supplied to infrared generator 228 will flow throughdistribution tube 230 faster than it would through a distribution tubeof the type shown in FIGURE 11 having the same overall dimensions. Thishigher velocity effects a more rapid transfer of heat from the walls ofthe distribution tube to the combustible mixture; and, therefore, for agiven rate of flow of combustible mixture to the burner, distributiontube 230 will remain cooler than a distribution tube of the type shownin FIGURE 11 with the same external dimensions and wall thickness.

Because of its smaller exposed surface area, less heat will betransferred to tube 230 than to a comparable tube of the type shown inFIGURE 11 in the same environment.

The insulating lining 234 further materially reduces the rate at whichheat is transferred from the ambient atmosphere to the interior ofdistribution tube 230 and, therefore, also assists in lowering thetemperature inside the tube so that, in a given environment, aninsulated distribution tube of the type shown in FIGURE 17 will have amuch cooler internal temperature than one of the type shown in FIGURE11. The smaller diameter tube, the decreased exposed surface area, andthe insulation, therefore, help to prevent distribution tube 230 fromoverheating and thereby prevent the flame adjacent the outer end 32 oforifice grid 38 from flashing back into the distribution tube.

The radiant grid 232 of infrared generator 228 has a generallyhorseshoe-like configuration provided by a grid 12 body 236 and integralmounting flanges 238 and 240. Radiant grid 232 is attached todistribution tube 230 by bolts which extend through aligned apertures242 in flanges 238 and 240 and are retained in place by retainers 106.

Venting apertures 244 through the wall of the body 236 of radiant grid232 permit combustion products to escape from the combustion zoneadjacent the outer end 32 of orifice grid 30 to the ambient atmosphereor into a suitable exhaust system.

Radiant grid 232 may be molded from refractory clay or may be formedfrom a cermet, solid quartz, quartz fibers, quartz cloth, or any otherrefractory material meeting the requirements of a specific application.

It is to be understood that it is not necessary to employ together thespecific insulated distribution tube 230 and ceramic radiant grid 232illustrated in FIGURE 17. Specifically, radiant grid 232 may be omittedto provide a line burner in accord with the principles of the presentinvention where the particular application requires direct flameradiation or convection by movement of the combustion gases, forexample. Also, refractory radiant grids of the type illustrated inFIGURE 17 may be employed with the types of distribution tubes describedpreviously to provide infrared generators in accord with the principlesof the present invention; and the metallic radiant grids of the typedescribed previously may be substituted for the refractory radiant grid232 in infrared generator 228 although, for some applications,refractory grids will prove more satisfactory.

In infrared generator 228 the combustible air mixture flows from theinterior of combustible mixture distribution tube 230 through orificegrid 30 and burns adjacent the orifice grids outer face 32. The burninggases heat the body of radiant grid 232 to incandescence andescapethrough vent apertures 244. Infrared radiation is emitted from theouter surface of the radiant grids body 236. Although the infraredgenerator 228 shown in FIGURE 17 is shown without reflectors, it is tobe understood that suitable reflectors for concentrating and directingthe emitted radiant energy of any of the several forms described abovecan be added to infrared generator 228, if desired.

Also, the configuration of the refractory radiant grid may be varied asdesired for particular applications. Examples of suitable alternateconfigurations are those disclosed in application No. 370,795, mentionedabove.

The combustible mixture distribution tube 246 shown in FIGURE 18 isidentical to the distribution tube 230 just described except that it hasa layer of insulation 248 on the outer surface of its main body portion250 rather than on its inner surface as in the embodiment of FIG- URE17. This distribution tube embodiment may, otherwise, be identical todistribution tube 230.

FIGURE 19 illustrates a combustible mixture distribution tube 252 whichis identical to the distribution tube 28 illustrated in FIGURE 1, forexample, except that a first layer of insulation 254 is applied to itsouter surface and a second layer of insulation 256 to its inner surfaceso that distribution tube 252 consists of a metal core sandwichedbetween inner and outer insulating layers, both of which act to reducethe transfer of heat from the ambient atmosphere to the combustiblemixture within the tube.

The insulation may be added to the distributor tube 252 in the mannerdiscussed above in conjunction with the embodiment of FIGURE 17. Ifdesired, distribution tube 252 may be fabricated with a relatively smallinternal cross section to reduce the heat transfer surface in contactwith the ambient atmosphere and to effect more efficient heattransferring high velocity flow of the combustible mixture through thedistribution tubes.

The infrared generators of the present invention have a number ofadvantages over those of the prior art including those infraredgenerators disclosed in the above- 13 mentioned copending applicationNo. 370,795. These include greatly improved efliciency which is due, inmain part, to:. (a) the advantages discussed above resulting from theemployment of line burners constructed in accord with the principles ofthe presentinvention; (b) the radiant grid configurations which permithigher temperatures to be attainedfor a given rate of fuel consumption;

(c) the flanged configurations of the fuel-air distribution tubes, whichprovide a more uniform distribution of the fuel-air mixture along thelength of the infrared generators; (d) the material reduction in heatdissipated by the fuel-air distribution tubes because of the narrownecks provided by the distribution tube flanges which separate the bodyof the tube from the combustion zone; (e) the substantial reduction inheat dissipation because of the inturned flanges or legs at the openside of the radiant members, which isolate the fuel-air distributiontubes from hot combustion products and from radiant heat; and (f) thenovel, improved reflectors, which effectively direct the radiant energyemitted from the radiant grids toward the area or objects to be heatedand efliciently eliminate heat losses due to stray radiation.

. The infrared generators of the present invention are also much moredurable than those mentioned above because .of: -(a) the novelarrangement for mounting the radiant grids, which permits them to movefreely as they expand and contract, and thereby prevents warping and, inaddition, minimizes conduction of heat from the radiant member to thefuel-air mixture distribution tube; (b) the use of comparatively shortradiant grids, which keeps expansion at a minimum; the additionalstrength gained by the' novel radiant grid configurations; (d) theincreased strength and rigidity of the novel fuel-air dis tributiontubes; and (e) the more secure method of attaching theradiatit grids tothe fuel-air distribution tubes. 7

Also, in the infrared generators disclosed herein, equipment failure dueto clogging of the orifice grid is eliminated as aproble'm since,because of the manner in which it is' attached, the orifice grid mayreadily be removed and replaced or cleaned. t

In addition, the infrared generators disclosed herein produce a highconcentration of radiant energy making radiant heating applicable toprocesses in which it was heretofore unusable. For example, by usinginfrared generators as disclosed herein spaced three inches on center,heat inputs of over 80,000 b.t.u. per hour per square foot of heatedarea can be obtained by operating the infrared generators at radiantgrid temperatures below 2,000 E, which is well below their maximum.Almost half of this heatinput is in the form of infrared radiation; andthis is within a few percent of the theoretical maximum amount ofinfrared radiation obtainable. Moreover, a higher proportion of theemitted radiation has wave lengths in the desirable 1 to 30 micron rangethan prior art infrared generators.

As mentioned previously, the line burners incorporated in the infraredgenerator illustrated in FIGURE 17 may be employed without radiant gridswhere direct flame radiation or convective heating by movement of theburning gases is required. Also, combustible mixture distribution tubesas shown in FIGURES 18 and 19 may be employed in line burners used assuch rather than being incorporated in infrared generators. Such burnershave all the advantages of the previously described embodiments asheretofore specifically enumerated. In addition, they are even moreeffective than the previously described embodiments in preventingoverheating of the distribution tube and the consequent flashback of theflame from the combustion zone into the tube. Therefore, line burnersemploying small tube diameters and insulating linings are especiallyuseful in applications where the burner is to be located in an extremelyhigh temperature environment. The same advantages are obtained when lineburners having insulated, small diameter distribution tubes areincorporated in infrared generators in accord with the principles of thepresent invention.

Both the line burners and the infrared generators as disclosed herein,in addition, are simple and are easily produced by mass productiontechniques. In all forms of the present invention except that of FIGURE17, they are constructed almost entirely from sheet metal and there areno castings, no machining required, no ceramic parts to handle, and aminimum of welding and other assembling steps to perform. Moreover, thesheet metal components are of simple configuration and can be readilyformed.

Furthermore, the novel line burners and infrared generators disclosedherein are extremely flexible and are adapted to many diverse types ofindustrial applications, to area heating, both indoors and outdoors, andto incorporation in heating plants such as warm air furnaces andboilers.

Other important advantages of the present invention will be fullyapparent to those skilled in the art to which it pertains from theforegoing detailed description of exemplary embodiments of theinvention.

The invention may be embodied in other specific forms without departingfrom the spirit or essential characteristics thereof. The presentembodiments are therefore to be considered in all respects asillustrative and not restrictive, the scope of the invention beingindicated by the appended claims rather than by the foregoingdescription, and all changes which come within the meaning and range ofequivalency of the claims are therefore intended to be embraced therein.

What is claimed and Patent is:

1. In an infrared generator of the combustion type:

(a) a fuel-air mixture distribution tube having opposed parallel flangesforming a passage communicating with the interior of said tube;

(b) an orifice structure between said flanges and extendingsubstantially the length thereof;

(c) a radiant grid of substantially the same length as said flanges,said grid having a flat perforate face, imperforate integral side wallsnormal to said perforate face, and integral, imperforate rear wallmembers extending at right angles to said side walls toward each otherand having a slot therebetween substantially equal in width to thepassage betweenthe distribution tube flanges; and

(d) means fixing said radiant grid to said distribution tube with thefree edges of said flanges and thefree edges of said rear wall membersjuxtaposed and the perforate face of said radiant member at right-anglesto said flanges and spaced from the free edges thereof.

2. The infrared generator of claim 1, together with insulating membersof substantially the same length as saiti1 radiant grid fixed to theinner surfaces of said side wa s.

3. In an infrared generator of the combustion type:

(a) a fuel-air mixture distribution tube having opposed flanges forminga passage communicating with the interior of said tube;

(b) an orifice structure in said passage between said flanges;

(c) a radiant grid of sheet metal formed into a tubular configurationextending substantially the length of said distribution tube, said gridhaving an apertured infrared radiation emitting front wall portion, anonapertured angular side and back wall portions, and integral flangesextending toward each other from opposite edges of said back wall andforming a slot therebetween substantially equal to the width of saidpassage between the distribution tube flanges; and

(c1) fastening means attaching one of said grid flanges to each of saiddistribution tube flanges with the grid flange free to movelongitudinally of the tube flange but restrained against movement towardand desired to be secured by Letters 15 away from the latter and withthe interior of said grid communicating with the passage between saiddistribution tube flanges.

4. A gaseous fuel line burner, comprising:

(a) a fuel-air mixture distribution tube having opposed flanges forminga passage communicating with the interior of said tube and extendingsubstantially the length thereof, the length of said passage beingsubstantially greater than the wall thickness of said tube;

(b) an orifice structure between said flanges;

(c) locating means preventing movement of said orifice structurelaterally of said flanges but permitting movement of said orificestructure longitudinally of said flanges, said locating means comprisingfastening members extending through and between said flanges andspanning the passage therebetween, said fastening members abutting theside of the orifice structure nearest the interior of said tube andthereby locating said structure relative to the interior of said tube,said locating means further including members bridging the flanges andfixed thereto on the side of the orifice structure opposite thefastening members and locating the orifice structure relative to the endof the passage between the distribution tube flanges most remote fromthe interior of the tube; and

- (d) clamping means including said fastening members operable toprevent all movement of said orifice structure relative to said flanges.

5. In an infrared generator of the combustion type:

(a) a fuel-air mixture distribution tube having opposed parallel flangesforming a passage communicating with the interior of said tube;

(b) an orifice structure between said flanges;

(c) a radiant grid extending along substantially the length of saidflanges and forming a combustion chamber around said orifice structure;

(d) reflector means including a pair of reflectors extendingsubstantially the length of said radiant grid and located on oppositesides thereof;

(e) fastening members extending between and through said flanges andsaid reflectors at intervals along said flanges;

(f) clamping means associated with said fasteners for clamping saidflanges against said orifice structure to retain said structure betweensaid flanges;

(g) means supported by said fastening members for fixing said radiantgrid relative to said flanges; and

(h) retainers on said fastening members for retaining said reflectorsthereon.

6. In an infrared generator of the combustion type:

(a) a fuel-air mixture distribution tube having opposed 16 flangesforming a passage communicating with the interior of said tube;

(b) an orifice structure in said passage between said flanges; I

(c) a radiant grid of sheet metal formed into a horseshoe configurationextending substantially the length of said distribution tube, said gridhaving an apertured infrared radiation emitting body and integralflanges extending toward each other from opposite edges of said body;and

(d) fastening means fixing one of said grid flanges to each of saiddistribution tube flanges with the interior of said grid communicatingwith the passage between said distribution tube flanges, said fasteningmeans comprising:

(e) fastening members extending between and through said flanges atintervals along said distribution tube; and

(f) inner and outer grid clips journalled on each of said fasteningmembers adjacent each of said distribution tube flanges, said inner andouter clips having cooperating legs adapted to embrace opposite sides ofthe flanges of said grid and cooperating portions adapted tosubstantially preclude lateral movement of said grid relative to theflanges of said distribution tube.

References Cited UNITED STATES PATENTS 233,389 10/1880 Adams. 1,727,5279/1929 Thurm 158l16 X 1,733,934 10/1929 Biers -5 126-92 1,978,17710/1934 Sweet 158113 X 2,443,101 6/1948 Flynn et a1 158116 2,543,6882/1951 De Coriolis et a1. 15899 2,884,998 5/1959 Taylor 1581 162,980,104 4/1961 Patrick et a1 158113 X 3,080,912 3/1963 Winter 158-116X 3,169,572 2/1965 Constance et a1. 12692 X FOREIGN PATENTS 448,960 6/1948 Canada. 651,426 10/ 1928 France. 651,540 10/1937 Germany. 170,64110/1921 Great Britain. 450,550 7/1936 Great Britain. 462,945 3/ 1937Great Britain. 512,431 9/ 1939 Great Britain. 904,792 8/1962 GreatBritain.

FREDERICK L. MATTESON, J R., Primary Examiner.

3. IN AN INFRARED GENERATOR OF THE COMBUSTION TYPE: (A) A FUEL-AIRMIXTURE DISTRIBUTION TUBE HAVING OPPOSED FLANGES FORMING A PASSAGECOMMUNICATING WITH THE INTERIOR OF SAID TUBE; (B) AN ORIFICE STRUCTUREIN SAID PASSAGE BETWEEN SAID FLANGES; (C) A RADIANT GRID OF SHEET METALFORMED INTO A TUBULAR CONFIGURATION EXTENDING SUBSTANTIALLY THE LENGTHOF SAID DISTRIBUTION TUBE, SAID GRID HAVING AN APERTURED INFRAREDRADIATION EMITTING FRONT WALL PORTION, A NONAPERTURED ANGULAR SIDE ANDBACK WALL PORTIONS, AND INTEGRAL FLANGES EXTENDING TOWARD EACH OTHERFROM OPPOSITE EDGE OF SAID BACK WALL AND FORMING A SLOT THEREBETWEENSUBSTANTIALLY EQUAL TO THE WIDTH OF SAID PASSAGE BETWEEN THEDISTRIBUTION TUBE FLANGES; AND (D) FASTENING MEANS ATTACHING ONE OF SAIDGRID FLANGES TO EACH OF SAID DISTRIBUTION TUBE FLANGES WITH THE GRIDFLANGE FREE TO MOVE LONGITUDINALLY OF THE TUBE FLANGE BUT RESTRAINEDAGAINST MOVEMENT TOWARD AND AWAY FROM THE LATTER AND WITH THE INTERIOROF SAID GRID COMMUNICATING WITH THE PASSAGE BETWEEN SAID DISTRIBUTIONTUBE FLANGES.